Answer:
Step-by-step explanation:
90+75=135
135-125
The two parabolas intersect for

and so the base of each solid is the set

The side length of each cross section that coincides with B is equal to the vertical distance between the two parabolas,
. But since -2 ≤ x ≤ 2, this reduces to
.
a. Square cross sections will contribute a volume of

where ∆x is the thickness of the section. Then the volume would be

where we take advantage of symmetry in the first line.
b. For a semicircle, the side length we found earlier corresponds to diameter. Each semicircular cross section will contribute a volume of

We end up with the same integral as before except for the leading constant:

Using the result of part (a), the volume is

c. An equilateral triangle with side length s has area √3/4 s², hence the volume of a given section is

and using the result of part (a) again, the volume is

Answer:
n=3
Step-by-step explanation:
Simplifying
8n + 12 + -5n = 21
Reorder the terms:
12 + 8n + -5n = 21
Combine like terms: 8n + -5n = 3n
12 + 3n = 21
Solving
12 + 3n = 21
Solving for variable 'n'.
Move all terms containing n to the left, all other terms to the right.
Add '-12' to each side of the equation.
12 + -12 + 3n = 21 + -12
Combine like terms: 12 + -12 = 0
0 + 3n = 21 + -12
3n = 21 + -12
Combine like terms: 21 + -12 = 9
3n = 9
Divide each side by '3'.
n = 3
Simplifying
n = 3